1. Interaction of Neuropeptides on Acetylcholing (ACh) Release: The neuropeptides to be examined include: mammalian bombesin, cholecystokininoctapeptide (CCK-OP), substance P (SP) and vasoactive intestinal peptide (VIP). Two different peptides will be used in combination in each of the experiments and the release of ACh from the myenteric plexus-longitudinal muscle strips will be measured by radiochemical and radioenzymatic methods. 2. Localizaiton of the action of Neuropeptides on Cholinergic Neurons: Neuropeptides listed in #1 will be examined on their ability to modulate ACh release from the isolated myenteric synaptic terminals (synaptosomes). Calcium dependence and requirement for depolarization (activation of Na+ channels) for peptide action will be examined. 3. Characterization of Opiate Receptors on Cholinergic Neurons: Receptors for opioid pepitides (enkephalins and endorphins) will be characterized in terms of the inhibition of ACh release from myenteric plexus neurons, both on basal and on peptide-induced ACh release. Specific blockers will be employed to determine the receptor subtype involved. 4. Mechanism of Release of Gut Neuropeptides: Specific release of neuropeptides in response to depolarizing agents will be examined, using a combined perfusion-chromatography method. ACh, ATP, serotonin and neuropeptides will also be used to elicit release. Quantitation of released peptides will be by RIA.